The cause is a Washington, D.C. holiday called Emancipation Day, which celebrates the end of slavery in the District of Columbia (which actually predated Abraham Lincoln's Emancipation Proclamation by nine months). It's usually celebrated on April 16, or the closest weekday, in this case, Friday, April 15.

And since federal law says that tax day must be either the 15th or the first succeeding day that isn't a Saturday, Sunday or holiday, that means tax day 2016 is April 18. Taxpayers in Maine and Massachusetts get an additional day, thanks to Patriot’s Day observances on April 18. Their taxes are due Tuesday, April 19.

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Now remember — before we go any farther — if you're sure you don't owe money, you do not need to file by April 18 (or 19!). Sure, you want to get your refund, but don't get bent out of shape or rush to the Post Office.

But if you do need to move ahead, here's our guidance on filing right.

Consider filing an extension. If you do owe tax, put those extra days to use. The penalty for turning in your federal return late is 0.5% of any unpaid tax due for each month or part of a month you're late. But you can put off filing your return — and avoid that penalty — by filing Form 4868, "Application for Automatic Extension of Time to File U.S. Individual Income Tax Return". You'll get an extra six months to submit your return without penalty.

But don't delay paying the tax bill. Any tax you owe is still due by April 18 (or 19th, in Maine and Massachusetts). The IRS also levies interest on unpaid taxes, currently at a rate of 3%, compounded daily.